A Study on Meso-β Scale System During An Excessive Heavy Rain

Affected by the outside of the typhoon 0012 (Prapiroon),an unprecedented heavy rain process,with the character of locality,intensity and abruptness,occurred in the northeast of Jiangsu from 0800GTM 30 to 0800GTM 31 August.The analysis indicates that the stable easterly stream provided by the second quadrant of the outside of the typhoon and its disturbance constitute the mesoscale easterly stream convergence line synoptic system which results in heavy rain.The high frequency quasi east-west and quasi south-north distribution of the mesoscale easterly stream convergence line and their substitution is in agreement with the high-frequency area where rain mass with rainfall≥10mm occurs.The analysis on the surface velocity advection divergence (F) shows that intense rain mass nearly accord with the severe center with F≥0,in other words,intense rain mass explodes in Xiangshui and its vicinities where convergence strengthens or intensively maintained.The results by further analysis and statistics suggest that the changes of the surface velocity advection divergence is closely associated with the maintenance of intense local rain mass and the reinforcement of rain intensity.

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